title: Ca(2+) signaling occurs via second messenger release from intraorganelle synthesis sites.
abstract: Cyclic ADP-ribose is an important Ca(2+)-mobilizing cytosolic messenger synthesized from beta-NAD(+) by ADP-ribosyl cyclases (ARCs). However, the focus upon ectocellular mammalian ARCs (CD38 and CD157) has led to confusion as to how extracellular enzymes generate intracellular messengers in response to stimuli. We have cloned and characterized three ARCs in the sea urchin egg and found that endogenous ARCbeta and ARCgamma are intracellular and located within the lumen of acidic, exocytotic vesicles, where they are optimally active. Intraorganelle ARCs are shielded from cytosolic substrate and targets by the organelle membrane, but this barrier is circumvented by nucleotide transport. We show that a beta-NAD(+) transporter provides ARC substrate that is converted luminally to cADPR, which, in turn, is shuttled out to the cytosol via a separate cADPR transporter. Moreover, nucleotide transport is integral to ARC activity physiologically because three transport inhibitors all inhibited the fertilization-induced Ca(2+) wave that is dependent upon cADPR. This represents a novel signaling mechanism whereby an extracellular stimulus increases the concentration of a second messenger by promoting messenger transport from intraorganelle synthesis sites to the cytosol.
authors.affiliation: Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, United Kingdom.
authors.forename: Lianne C
authors.initials: LC
authors.lastname: Davis
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Morgan
authors.forename: Margarida
authors.initials: M
authors.lastname: Ruas
authors.forename: Julian L
authors.initials: JL
authors.lastname: Wong
authors.forename: Richard M
authors.initials: RM
authors.lastname: Graeff
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Poustka
authors.forename: Hon Cheung
authors.initials: HC
authors.lastname: Lee
authors.forename: Gary M
authors.initials: GM
authors.lastname: Wessel
authors.forename: John
authors.initials: J
authors.lastname: Parrington
authors.forename: Antony
authors.initials: A
authors.lastname: Galione
mesh_terms: D036541:ADP-ribosyl Cyclase / Q000235:genetics / Q000378:metabolism*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D020013:Calcium Signaling; D003001:Cloning, Molecular; D036563:Cyclic ADP-Ribose / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005089:Exocytosis; D055354:Exosomes / Q000378:metabolism*; D005306:Fertilization; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D033704:Nucleotide Transport Proteins; D010063:Ovum / Q000378:metabolism; D047270:Strongylocentrotus purpuratus / Q000201:enzymology / Q000235:genetics
chemical_list: D033704:Nucleotide Transport Proteins; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D036541:ADP-ribosyl Cyclase